Method for the manufacture of filters composed of cellulose acetate



Jan. 16, 1962 R. T. CRAWFORD ET AL 3,017,309

- METHOD FoR THE MANUFACTURE oF FILTERS coMFosED oF cELLuLosE ACETATE 2 Sheets-Sheet 1 Filed Feb. 21, 1 957 MESES n zhz S m m M Y.: O mmm M S W 0 TB 0 U ma w A 0 @J R Y B hm.

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Jan. 16, 1962 R. T. CRAWFORD ET AL 3,017,309

METHOD FOR THE MANUFACTURE oF FILTERS coMPosED OF CELLULOSE ACEITATE Filed Feb. 2l, 1957 2 Sheets-Sheet 2 kwlvm Mkkwk TUB HUBERT I'. CRAWRD JOEL B. SIMS v INVENTORS BY i* K A'I'TORISTE'YS` United States This invention generally relates to tobacco smoke filters which may be employed as cigarette or cigar filter tips or as filters for use with cigarette or cigar holders or with pipes. More particularly the present invention relates to an improved and inexpensive process for making such tobacco smoke filters from a plurality of cellulose acetate bers initially in the form o-f rela-tively highly crimped continuous filament tow in which the filaments are in substantial aligned relationship.

The processes which were employed prior to our invention for the conversion of such ya continuous filament tow of cellulose acetate into tobacco smoke filtering material did not provide the quality and character of product which was desired by the tobacco industry.

The tobacco industry desires a uniformly constructed cellulose acetate filter which can be' made rapidly and easily, and of a uniformity within close tolerance limits, from crimped continuous filament cellulose acetate tow as received from the tow manufacturer. filter should be distinctive as respects such characteristics as compactness, size, weight, density, fiber distribution, air pressure drop, resiliency, body, rigidity, fiber loss, porosity and integrity. These distinctive characteristics should be combined in a manner so that the resulting filter not only does not detract from the smokers pleasure, but gives the assurance that the filter is functioning properly to remove any harmful ingredients present in the tobacco smoke. In the cigarette manufacturing industry, yan economic requirement is that the completed filter is so constructed as to be easily assembled with the cigarette in processing apparatus conventionally used in. they industry for cigarette manufacture and packaging.

An object, therefore, of the present invention is to provide a high speed, efficient process suitable for carrying out the conversion of crimped continuous filament tow, in the compressed condition it is received from the producer, into filter units of substantially uniform characteristics which are excellent as tobacco smoke-filters.

Another object of this invention is to provide a novel process for the conversion of crimped continuous lament cellulose acetate tow into a compact homogeneous unit of cellulose lacetate filaments from which improved tobacco smoke filters can be made.

Another object of this invention is to provide a novel process for Ithe conversion of crimped continuous filament cellulose acetate tow into a wrapped filter unit having a uniform cross-section characterized by the lack of filament bundles and undesirable non-uniform channels therein.

Other objects will appear hereinafter.

In accordance with the present invention we provide a continuous process by which the foregoing objects are efficiently attained. Our novel continuous process for the conversion of relatively highlycrimped continuous filament cellulose acetate tow into tobacco smoke filter units preferably comprises the successive continuous steps of:

(1) Stretching the crimped tow longitudinally to teln-v porarily straighten out the crimps therein;

(2) Expanding the cross-sectional dimensions of th tow` by abruptly relaxing the tension on the tow;

(3) Spreading the tow to y'ar ribbon-like band having a The desired.

atent 3,017,309 Patented Jan. 16, 1962 2 width considerably greater than that of the expanded tow;

(4) Treating the ribbon-like band with a bonding medium;

(5) If required, adding finely divided powder-like filtering material to the ribbon-like band;

(6) Condensing the treated tow to a firm, compact, rod-like `form having a diameter slightly smaller than that of a cigarette;

(7) Wrapping and sealing the condensed tow in a suitable wrapper;

(8) Heat-treating the wrapped rod of condensed tow so that the bonding medium is caused to stiffen on the wrapped rod;

(9) Cutting the stiffened wrapped rod into lengths suitable for filter u nits.

The filter unit may then be assembled in the cigarette by aA standard process,

Our novel process as indicated above preferably empoys as a starting material a relatively high crimped continuous filament cellulose `acetate tow. The term tow describes a large number of aligned, continuous filaments which are associated in a somewhat loose form fiat bandlike structure. When this tow is crimped the product is crimped tow. This type of crimped tow isnow available on the market as EstronTow. The size of the filaments in the tow is designated by the term denien Denier is the weight in grams of a 9,000 meter length of yarn. For example, a -fiament 9,000 meters long which weighs 1 gram is designated 1 denier. The size of the tow is given in total denier. Total denier is the product of the denier per filament (d./f.) times thenumber of filaments contained in the tow.' Thus,.a 5 d./f., 80,000 denier tow would contain 16,000 filaments and would weigh 80,000 grams per 9,000 meters.

The preferred crimped continuous tow is valso one which has been treated to impart desirable density characteristics thereto. The crimped continuous filament cellulose acetate tow most suitable for use in the process of the instant invention is one that has been conditioned with a lubricant whichimparts additional density and lubricating properties to the tow but without giving the tow additional anti-static properties. Thus, the crimped cellulose acetate tow although lubricated so that it may pass easily through the steps of the process preferably carries a staticcharge which, due to electrostatic repulsion between filaments, assists in the step of filament separation and distribution which, as is described hereinafter, is carried out primarily by other means. ,A preferred lubricant is a' neutral, non-toxic material. Most advantageously we employ'about 0.5% of pharmaceutical grade mineral oil by weight of the fibers.

Tows suitabl'efor cigarette filters range from 45,000 to 160,000 total denier. The filament sizes normally available are 1.5, 3, 5,8, 12, 16,20 and 35 denier per filament and the tow may be made up between 5,000 and 100,000 filaments (preferably 20,000) of about 1.5 to 16 (preferably about 5) denier per filament or atotal denier within the range of 80,000 to 250,000 (preferably 100,000). The crimps in the tow should range from 4 to 18 crimps per inch and 9 crimps per inch are preferable.

The preferred Estron Tow comprises continuous filaments of celfulose acetate which have been spun from a spinnerette, having a plurality of orifices therein, by the well-known dry spinning process and loosely drawn to` get'her in more or less parallel band-like association to form a continuous band which is termed a tow in the spinning industry. Suchv a cellulose acetate tow can be made, for exampe, by the dry spinning process described in H., G. Stone Patents 2,000,047 and 2,000,048. The cellulose acetateY from which the tow is manufactured may'have an acetyl Value of 38 to 41%, preferably 38.8

to 39.2%. The tow may be crimped by any suitable crimping process which can give the desired highly crimped filament tow. The tow may be advantageously supplied for use in our process in the form of a bale about 40 inches high, 25 inches wide, an'd 50 inches long which weighs 600 to 800 pounds. Such a bale contains a continuous tow of about 91,000 feet in length which is normally enough to supply the process for about 8 hours when making 1,000 filter tips per minute.

The various steps in the process maybe carried out in any suitable device. A very satisfactory device for this purpose is shown in the accompanying drawings in which:

FIG. 1 is an isometric drawing of apparatus which may be employed for carrying out our method of processing tow up to the point where the processed tow is fed to the machine for forming it into a round wrapped rod;

FIG. 2 is an isometric drawing of the apparatus for wrapping the processed tow into a continuous wrapped rod and cutting the rod into filter units;

FIG. 3 is a vertical section showing the interior construction of the banding jet taken on the lines 3--3 of FIG. 1;

FIG. 4 is an enlargedlongitudinal section through a portion of a tipped cigarette assembled with a filter made by the instant process.

Referring to FIG. l, there is shown one form of apparatus suitable for carrying out our improved method for processing cellulose acetate tow into filter units for use with cigarettes. As shown in this drawing, a bale of crimped continuous filament tow is positioned so that the tow 11 may be continuously supplied to the smoke filter making process.' The tow in the bale is in a relaxed condition so that it retains all the crimp, thus giving greater bulkiness to the tow. Tow 11 passes between a pair of flat plates one of which is numbered 13 which act to flatten out tow 11 somewhat and then contacts guide 14 and passes over guide 15 and continues to the next step of the process.

It has been found that a constant rate of withdrawal with well-controlledtension is desirable for the formation of the uniform band of filaments required for subsequent processing steps.

The next step in the process stretches the tow 11 so as to temporarily straighten out the crimps therein without stretching the crimps beyond their elastic limit. As shown in FIG. 1, this crimp stretching step may be carried out by two pairs of coacting rolls 16 and 17 which are preferably rubber covered so as to improve the traction on the tow passing therebetween. The tow 11 passes between the rolls of each pair. Rolls 17, which are positively driven by drive Vmeans 18, are driven at a faster rate than rolls V16 so that the above-described step of temporary stretching of tow 11 takes place in the zone between the respective nips of rolls. A tension of 20 to 250 pounds may be advantageously imparted to the tow 11 duringthe stretching step. A mechanical vibrator 19 actuated by means, not shown, is positioned below the tow 11, and while the tow is under tension it may, if desired, be struck by the vibrator 19 at a frequency, for example, of 1800 times per minute. As shown in the drawing, the rolls 16 and 17, drive means 18 and vibrator 19 may be suitably mounted on member 21.

The next step of the process takes place as the stretched tow leaves the nip of the pair of rolls 17. The tow at this point is conducted onwardly at 'a considerably less tension and this results in permitting the crimps f which were stretched by the previous step of our process'suddenly to reform. This sudden relaxation of the tension with the accompanying spring-like action of the reforming crimps permits an explosive expansion within the somewhat flattened tow to restore it to a more cylindrical shape. 'Ibis advantageously results in arranging the fibers to give a tow of substantially homogeneous cross-section.

By these two consecutive steps of stretching the crimped tow and then permitting the crimps suddenly to be restored, any filaments which previously may have been associated here and there within the tow in heterogeneous bundles are separated and the bundles are thus eliminated. This elimination of thevbundles perforce also eliminates undesired channels which often occur within the t'ow cross-section adjacent to the unwanted bundles 'of filaments. A tobacco filter containing such random positioned bundles and channels obviously will not have the desirable uniform filtering characteristics previously described in the above paragraphs.

The tow which now has the plurality of crimped continuous filaments homogeneously distributed in parallel relationship continues to the next step of our process. This next process step comprises acting on the expanded tow to spread it into a substantially flat band. This spreading step may be conducted in any suitable manner. We have found, however, that carrying out this step of our process in a banding jet device such as described below is advantageous. Therefore, as shown in FIG. l, the expanded tow 11 proceeds to such a banding jet device 22.

As shown more clearly in the sectional view of FIG. 3, the banding jet 22 is in the form of a hollow box-like member 23 having a plenum chamber 24 therein which is connected by pipe 25 to a source of air under pressure. The top of the chamber 24 is defined by slotted plate 26 having a plurality of air jet slots 27 therein. The end walls of this banding jet 22 extend above plate 26 and a solid cover plate 28 is fitted thereon. The side walls, not shown, merely enclose chamber 24. Thus a slot-like chamber 29 is formed between slotted plate 26 and cover plate 28. Slots 31 and 32 shown in FIG. 1 are positioned in the respective side walls of banding jet '22 to permit the tow 11 to move through chamber 29.

The air from jets 27 strikes the tow substantially perpendicularly to its path of movement and acts to flatten the tow and to spread apart the filaments, thereby forming a band. We have found it desirable that this band be approximately eight times the original tow width and be also of a minimum thickness commensurate with such a width. In this thin, spread out condition the several filaments of the tow are accessible to treatment with fluids which are applied thereto by the next step of our process.

In the next step, the moving tow now in the form of the fiat band of parallel disposed crimped filaments is continuously sprayed on each side with a fluid bonding medium. Most advantageously the spray is a liquid plasticizer which will produce a tackiness in the filaments through surface solvation thereof at points of contact therewith. While various devices may be employed to apply the plasticizerV to the band, the apparatus shown in FIG. 1 is quite effective. As there shown, the tow on leaving the banding jet apparatus 22 enters spray chamber 33 which may be glass enclosed and be provided with an exhaust flue 34. In the spray chamber 33 a fluid plasticizing bonding medium is applied by oppositely disposed spray guns 35 and 36 to cause the filaments to be capable of bonding to an adjacent filament wherever contacted by the spray.

The plasticizer is sprayed so as to form minute droplets at random points along the top and bottom surfaces of substantially each of the filaments of the two in sufficient quantity so that substantially each of the filaments will have a plurality of bonding points along any length corresponding to the length of the smoke filtering unit which is-to be the ultimate product. Most advantageously, a plasticizing agent such as methyl phthalyl ethyl glycolate (carbethoxymethyl methyl phthalate) is employed. Other suitable nontoxic plasticizers which have nontoxic decomposition products and do not adversely affect the taste of tobacco smoke filtered through elements of the invention, are dibutyl phthalate, tripropionin and acetyl triethyl citrate. The plasticizing agent preferably is sprayed on until the fibers contain 4 to 30% (preferably about 6-15%) by weight of plasticizer. If

`shown at 49 The powder spray isshown at 51.

desired, the temperature at which the fluid treatment takesv place may be controlled by means, not shown.

The tow now having the plasticizer therein may be conducted directly to the apparatus shown more completely in FIG. 2 for wrapping the tow into continuous filter rodsand for other processing to be described subsequently.

However, in certain instances Vit may be desired to apply one or more additions to the plasticized tow. The plasticized tow is an excellent carrier for a number of materials whichl may be added to alter the fiavor or to varythe filtration characteristics. Therefore, as shown in FIG. 1, the spread-out tow which has been given the sprayed plasticizer treatment in chamber 33, on leaving that, chamber is conducted into a dusting process which may.- beV suitably conducted in dusting apparatus 37. The dusting apparatus 37 comprises an enclosed chamber 38, the bottom.l of. which comprises a hopper 39 into-which the. powder to be added to the plasticized tow is fed' from b in- 41 by screw 42. The powder is supplied` to` the underside of the plasticizedtow by blower 43. and duct 44 to nozzle 45,; and tothe upper side of the tow Aby blower 4,6,A duct 47 and nozzle 4,8. The blowersare operated by electric motors, one ofv which is The upper wall of the closed chamber 38 is formed by a pressure rupturable foil,k the edgeof which is shown vat 52; An explosion directing shield 53 is positioned above the foil; sealg52 and; chamber 3S which is closedv thereby. The side walls of the chamber, one of which is shown bnokenawayy at 54, maybe of metaLor glass.

To prevent dust from. leaving the. dust chamber 38 through the slots by ,whichI the tow 1-1 enters and leaves the; chamber 38, suction. devices 55 and 56. are provided. rl `hesesuction devices are afiixed respectively to the end fwall's, of the, dust chamber 38' and comprises-elongated 4 suction chambers in fluid communication with chamber 3,8. The; tow 1-1 enters one side of suction device 5S through a slot having a length substantially equal tothe widthof the tow anda width,y substantially the thickness of the tow andY leaves ,throughV a similar slot which is tightlyy positioned againstV a similar-slot in thev adjacent wall of chamber 33. Asis apparenty from FIG. 1, scavenging ducts, 57 and 53. respectively produce a suction ini suction devices 5,5 andf. Thus any dust particles l hydroxyethyl` cellulose, and calcium stearate `may be. ernl ployed as additives..

On leavingrthe dustingv chamber 3S the tow passes between delivery i'olls 59 and 61 which areturned by driving ymeans 40.

It will now be apparent thatdriven rolls 17 cause the tow 11` to unwrap from bale 1t)` and that rolls59 and 6.1`v provide the drawing for. pullingthe towv 11 throng the plasticizingand .powder applying stations.` f

The treated continuous filament cellulose acetate tow is now. in conditionr to be, formed into. cigarette filter units The tow 11 is therefore introduced into the filter formingv devices through condensing trumpet 62 whichl reforms, theflat tow 11v to a roundgmultiple filament-,strand 63. l

Av device suitable for, carryingl out the wrapping` of i the round-strand 63- into a filter unit islshown in FIG; 2. In ,additionio the above-mentioned tow condensing trumpet162,1 the devicel comprisesv an endlessV belt 64 which revolvesy arounddrumsa.v 65. and 6 6, and is maintained taut by drums 67. The belt is driven by means, not shown. The wrapper 69, which may be filter paper, is continuously unwound from roll GS and passes over guide roll 71 and is carried by endless belt 64 through a wrapper forming device 72 which bends the wrapper into a U- shaped form just before it comes into contact with the strand 63. The U--shaped wrapper containing the strand 63 is now carried by endless belt 64 through a second forming device 73 in which the wrapper is lapped around the strand 63 leaving one edge 74 of the paper extending upwardly.

The standing edge 74 of the paper then moves along to contact rotating wheel 75 which applies a suitable adhesive to the inner side of the standing edge 74. The source of the adhesive is not shown. The standing edge '74 is now smoothed down over the adjacent paper edge by forming member 76 and is then heat sealed into a permanent adhesive bond by electric heating shoe 77.

The product therefore at this point in the process is a continuous round and compact filter rod 78 having a diameter slightly lessthan that of the cigarette with which the filter is to be assembled.

If desired, the filter rod '78 may be stiffened by heat treatment as by being passed through an electrically heated die 79. The heat treatment may be conducted at 160 F.

The continuous heat treatment of the paper covered rod may be replaced by subjecting the severed rods to heat treatment such as by storage in a chamber heated to 200 F. for a period of about two hours. In such case, we have found it satisfactory to subject the finally wrapped rods of cellulose acetate filaments to a temperature of 160 F. forfour hours where solvation has beenaccomplished with a plasticizer such as Monsanto Santicizer M-l7 (believed to be carbethoxymethyl methyl phthalate),v although the treating time may be varied from 1/2 to 24 hours depending on the temperature and the particularplasticizing agent employed. A temperature within the range of F.to 300 F. may be found satisfactO K lli" sometimes may be satisfactory to forego a final heat treatment and merely to allow the paper-wrapped rod to age for a period of 24 hours to allowv the plasticizer to penetrate and the bonding to become thorough. and` com-v mass which facilitates handling and assembly operations.

On leaving heated die 79, the filter rod 7S is cut into appropriate lengths by cutter Sl which isl rotated by means, not shown.

After the paper-covered rod has been severed into elements of appropriate length and preferably stiffened as bythe heat treatment, the elements may be employed as the final product for use in pipes and cigarettes and cigar holders. If the filter material is to` be used as a tip for cigarettes, known procedures for manufacturing filter tip cigarettes may be'used. That is to say, elements of appropriate length may be fed toa joiner or other machine which serves to position the-filter elements adjacent to tobacco bodies, join themV and cut the joined pieces at the proper points.

The product produced in accordance with the present invention is an article ofmanufacture lor smoking device containing' the same, v. the article comprising a rod,` normally cylindrical in form andA customarily substantially the size ofa cigarette in circumference and diameter, the rod being a compact, rigid, structurally unitary debundlized mass of crimped cellulose acetate filaments and a wrapper encircling the mass, each filament of the mass being substantially coextensive therewith. The filaments as a Whole are in substantial alignment longitudinally of the mass 'out substantially each of the individual filaments has non-oriented short portions thereof disposed randomly in diverging and converging relationship to the main lament axis. Substantially all of the filaments of the mass are positively bonded to contiguous filaments within said structurally unitary rod by means of surface solvation bonds at random points of contact of the filaments. The filaments of the mass are uniformly distributed throughout the transverse section of the mass thereby providing uniform filtering. FIG. 4 shows the filter unit assembled in normal position with a cigarette. he filters are usually mm. in circumference and 13 mm. long.

While our process can be carried out on the apparatus disclosed in the foregoing paragraphs, it should be mentioned that our process can be carried out with different apparatus. For instance, in the step of filament separation, tow opening may be accomplished by use in cooperation with a pair of drive rolls of a trap box having a weighted tongue to produce a braking action. The trap box would be a substitute for the pair of bralced idler rolls 16. In other words, an opening device instead of two pairs of tension rolls might comprise a pair of driven rolls and a retarding device such asia tongued-trap box. Banding might be accomplished successfully through the use of an expander bar as known in the art or as suitably modified. Thus one might employ a banding device comprising a surface presenting a portion of a cylinder and provided with two diverging sets of tow contacting ribs at an angle to each other of, eg., 60. With such a device it is contemplated that tow passing over the bar and in frictional engagement therewith will be banded in a manner similar to that occurring in the banding jet in that filaments would be transversely moved apart from each other, particularly in regions of high filament density to produce a tow structure having a greatly increased uniformity of cross-sectional fiber distribution.

This application is a continuation-in-part of our copending application Serial No. 374,168, filed August 14, 1953, now Patent No. 2,794,480 of June 4, 1957, and entitled Apparatus for the Manufacture of Filters Composed of Cellulose Acetate.

We claim:

l. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multililament tow, the filaments of which have a plurality of crimps therein, stretching the tow under a tension suflicient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension thereby permitting said crimps freely to reform, spreading the: thus expanded tow to a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spreadout tow with a bonding medium, condensing lsaid treated tow to a substantially round rod-like form and wrapping and sealing the condensed tow in a thin wrapper.

2. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament tow, the filaments of which have a plurality of crimps therein, stretching the tow lengthwise under a tension suficient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension thereby permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbonlike band in which the individual filaments are in substantial parallel relation with each other, having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, condensing said treated tow to a substantially round rodlike unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiften the unit and cutting the rod-like unit into individual filter elements.

3. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament crimped tow, the filaments of which have av plurality of crimps therein, stretching the tow lengthwise under a tension sufficient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension thereby permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, adding a powder-like filter aid to the surface of the spread-out tow, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiten the unit, and cutting the rod-like unit into individual filter elements.

4. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament crimped tow the substantially parallel filaments of which have from 4 to 18 crimps per inch therein, stretching the tow lengthwise under a tension sufficient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension thereby permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiffer! the unit, and cutting the rod-like unit into individual filter elements.

5. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament crimped tow, the substantially parallel filaments of which have approximately nine crimps per inch therein, stretching the tow lengthwise under a tension sufficient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxingfsaid tension thereby permitting ysaid crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a non-toxic bonding medium, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiffen the unit, and cutting the rod-like unit into individual filterelements.

6. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament crimped tow, the substantially parallel filaments of which have from 4 to 18 crimps per inch therein, stretching the tow lengthwise under a tension sufficient to straighten out temporarily said crimps, expanding the'cross-sectional dimensions of the tow by abruptly relaxing said vtension thereby permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, adding a powder-like filter aid to the surface of the spread-out tow, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unitin a thin wrapper, heat treating the wrapped rod-like unit to stiften the unit, and cutting the rod-like unit into individual filter elements.

7. A continuous process for forming unitary rod-like filter elements which comprises providing a continuous multi-filament crimped tow, the `substantially parallel 9 lfilaments of which haveapproxirnately nine crimps per inch therein, stretching the tow lengthwise under a ten'- sion sufiicient to straighten out temporarily lsaid crimps, expanding the cross-sectional dimensions of the towby `abruptly relaxing said tension thereby permitting Asfai'd crimps freely to reform, spreading thethus expanded tow in a sidewise direction to form a'ribbon-lik'e, band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, adding a powder-like filter aid to the surface of the spread-out tow, condensing saidtreated tow to a substantially round lrod-like unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiten the unit, andcutting greater than that of said expanded tow, treating the thus v spread-out tow with a bonding medium, condensing said treated tow to a substantially round rod-likeform and wrapping and sealing the condensed tow in a thin wrapper.

9. A continuous-process for forming unitary rod-like filter elements which comprises providing a continuous multifilament tow, the filaments of which have a plurality of crimps therein, placing a static charge on the tow, stretching the tow lengthwise under a tension sufiicient to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension and permitting the static charge on the tow to separate the relaxed filaments thereby permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to form a ribbonlike band in which the individual filaments are in substantial parallel relation with each other, having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, condensing said treated tow to a substantially round rodlike unit, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to stiften the unit and cutting the rod-like unit into individual filter elements.

10. A continuous process for forming unitary rod-like filter elements which comprises providing a continuousA multi-filament crimped tow, the filaments of which have a plurality of crimps therein, placing a stat-ic charge on the tow, stretching the t-ow Ilengthwise under a tension sufiicien-t to straighten out temporarily said crimps, expanding the cross-sectional dimensions of the tow Iby, abruptly relaxing said tension thereby permitting the static cha-rge on the tow to separate the relaxed filaments while permit-ting said crimps freely to reform, spreading the thus expanded tow in -a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating `the thus spreadout tow with a bonding medium, adding a powder-like filter yaid to the surface of the spread-out tow, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unit in a thin wrapper, heattreating the wrapped rod-like unit to stiften the unit, and cutting the rod-like unit into individual filter elements.

11. A continuous process for forming unitary `rod-like iilter elements which comprises providing a continuous multi-filament crimped -tow the substantially parallel iilaments of which have `from 4 to 18 crimps per inch therein, placing a static charge on the tow, stretching the tow llengthwise under 'a tension sufiicient to straighten an tenaerariiyeia erimpssxpanamg the dess-'Sections dimensions of the tow jbjy vabruptly relaxing said tension thereby permitting y'the .static 'charge on the tow to s'ep- Ya-'rat-e the relaxed filaments' while permitting s'a-id crimps unit in "a thin wrapper, heat treating the wrapped rod- '.'like unit to stiften the unit, and 'cutting the `rod-like unit -irito individual filter elements.

, 12. Acont'inuous process for forming "unitary rod-like filter elements which comprises providing Ia continuous multi-filament crimped tow, lthe Vsubstantially parallel lainent's of "which 'havea'pproximately nine crimps per inch therein, placing astatic charge on the tow,` stretching the tow lengthwise under a tension sufiicient to straighten 'out l rrnporarilyfs'aid crimps,jexpanding ythecross-sectional sions of the tow by abruptly 'relaxing said tension 'and permitting the stati'ccharge 'on the tow to 'separate l the relaxedy filaments ffth'er'eby permitting said crimps freely to reform, spreading "the thus expanded tow -in a sidewise direction to form a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a b-onding medium, condensing said treated tow to' a substantially round rod-like uni-t, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit t-o stiften the unit, and cutting the rod-like unit into individual filter elements.

13. A continuous process for -forming unitary rod-like filter elements which lcomprises providing a continuous multi-filament crimped tow, the substantially parallel laments of which have from 4to 18 crimps per inch therein, placing a 4static ch-arge on the tow, stretching the tow lengthwise under a tension sufiic-ient to straighten out temporarily said crimps, expanding the cross-sectional di-V mensions of the tow by abruptly `relaxing said tension and permitting the static charge 'on the tow to separa-te the relaxed filaments thereby permitting said crimps freely to reform, spreading the thus expanded tow in a `sidewise direction to form -a ribbon-like lband hav-ing a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium, adding a powder-like filter aid to the surface of the spread-out tow, comdensing said treated tow to a substan-tially round rod-like unit, wrapping yand sealing the rod-like unit in a thin wrapper, heat treating the wrapped Y rod-like unit to stien the unit, and cut-ting the rod-like u-nit into individual filter elements.

14. A continuous process for forming unitary trod-'like filter elements which comprises providing a continuous multi-filament crimped tow, the substantially parallel filaments of which have approximately nine crimps per inch therein, placing -a static charge on the tow, stretching the tow lengthwise under a tension sufficient tostraighten out temporarily said crimps', expanding the cross-sectional dimensions of the tow by abruptly relaxing said tension.

thereby permitting the static charge on t-he tow to separate the relaxed filaments while permitting said crimps free-ly to reform, spreading the thus expanded tow in a sidewise direction to form. a ribbon-like band having a width considerably Vgreater than that of said expanded tow, treat-ing the thus spread-out tow with a bonding medium, adding -a powder-like filter aid to` the surface of the spread-out tow, condensing said treated tow to a substantially round rodlike uni-t, wrapping and sealing the rod-like unit in a thin wrapper, heat treating the wrapped rod-like unit to st-iffen the unit, and cutting the rod-like unit into individual filter elements.

l5.. A continuous process for forming unitary rod-like filter velements which comprises providing a continuous multi-filament cellulose acetate crimped tow, the subtow, stretching the tow lengthwise under a tension suficient to straighten out temporarily said crimps, exv panding the cross-sectional dimensions of the tow by abruptly relaxing said tension thereby permitting the static charge `on the tow to separate the relaxed filaments while permitting said crimps freely to reform, spreading the thus expanded tow in a sidewise direction to yform a ribbon-like band having `a width considerably greater than that of said expanded tow, treating the thus spreadout tow with a bonding medium, adding a powder-like `filter 4aid to the surface of the spread-out tow, condensing said treated tow to a substantially round rod-like unit, wrapping and sealing the rod-like unit in -a thin wrapper, heat treating the wrapped rodlike unit to stiften the unit, and cutting the rod-like unit into individual filter ele ments.

16. A continuous process for forming unitary rod-like filter elements whichv comprises providing a continuous multi-filament tow, the filaments of which have a plurality of crimps therein, stretching the tow under a ten- `,ion suicient to straighten out temporarily the crimps,

12 expanding the cross-sectional dimensions of the tow by abruptly relaxing said ten-sion'thereby permitting said crimps to reform, spreading the thus expanded tow-to a ribbon-like band having a width considerably greater than that of said expanded tow, treating the thus spread-out tow with a bonding medium comprising a glyceryl triester ofV 'a Ilower fatty acid, condensing said treated tow to a substantially round rod-like form and wrapping and sealing the condensed tow in a thin wrapper.

References Cited in the file of this patent UNITED STATES PATENTS 2,336,745 Manning Dec. 14, 1943 2,369,462 Hurst Feb. 13, 1945 2,399,258l Taylor Apr. 30, 1946 2,644,780 Simkins et al. July 7, 1953 2,707,308 Taylor et al. May 3, 1955 2,774,680 Hackney et al Dec. 18, 1955 2,789,563 Taylor et al Apr. 23, 1957 2,790,208 Smithv Apr. 30, 1957 2,793,572 Parmele May 28, 1957 2,794,480 `Crawford et al. June 4, 1957 2,796,810 Mul-ler June 25, 1957 

1. A CONTINUOUS PROCESS FOR FORMING UNITARY ROD-LIKE FILTER ELEMENTS WHICH COMPRISES PROVIDING A CONTINUOUS MULTIFILAMENT TOW, THE FILAMENTS OF WHICH HAVE A PLURALITY OF CRIMPS THEREIN, STRETCHING THE TOW UNDER A TENSION SUFFICIENT TO STRAIGHTEN OUT TEMPERARILY SAID CRIMPS, EXPANDING THE CROSS-SECTIONAL DIMEMSIONS OF THE TOW BY ABRUPTYL RELAXING SAID TENSION THEREBY PERMITTING SAID 